The paper “Millimeter-Wave Folded Reflector Antennas with High Gain, Low Loss, and Low Profile” by Wolfgang Menzel, Dietmar Pilz and Maysoun Al-Tikriti, June 2002 in the IEEE Antennas and Propagation Magazine, Vol. 44, No. 3, pages 24-28, describes applying reflective metal structures to a circuit board in order to construct a reflector antenna for millimeter waves.